So, I was searching for a headphone amp for what seems like four years. With so much stuff coming out in the past decade the options have become near ludicrous. My needs were "fairly" simple: Neutral sound signature, class A circuit topology and the one aspect that kept me waiting so long, fully differential in and out, meaning a true balanced signal from input to my headphones. I heard about this little amp about two years ago and put off buying it until now.
The build of this amp is as solid as it is sturdy(oh my God I fear for that tiny gain switch) and well vented as this little thing could adequately heat a drink sitting on the top plate. The volume is not indicated well in low light, but using the volume knob itself feels like a quality volume pot, so smooth and linear. My DAC is also a recently purchased SMSL SU-8 which includes balanced outs and a dynamic range of 120 db with a respectable SNR of 116 db. I have only driven my headphones through the single ended output as I am saving again to buy balanced cables for each set I have: HD 600, HD800 and M1060. With the DAC and amp paired together via xlr cables, the overall noise floor is virtually undetectable. Dead silent. Not even the highly sensitive HD 800 can be heard over this pairing.
Here comes the honesty. Normally, I have driven my headphones out of my vintage receiver. The benefit of doing that was I had all the power to drive the M1060's with a built in graphic equalizer to help tame the treble on the HD 800's. My receiver also has a loudness control feature which basically amplifies the lowest and highest frequencies, to my ears, about 8-10 db. When this is off and the equalizer is leveled out the sound is dead neutral. Upon listening to my first set of tracks on the HPA-3B I noticed the amount of bass was on par with the receiver with the aforementioned features turned off. The bass is lean overall but present. The midrange, to me, sounds forward and at times a bit shouty but is smooth and resolving with the right music. Treble decay is airy and natural but more so when compared to my receiver. Class A topology allows for that extra bit of fidelity that class A/B(the receiver) just can't reach.
I use foobar2000 with an equalizer(when you own HD 800's or you're a nit picker in general it's a must) and so far I'd say the dac and amp sound great together. Until I get some balanced cables I can only enjoy single ended for now. I hope to add some updates in the future.

The matrix has all neutrik connectors a Nortel torodial transformer wima caps and high grade nichicon audio capacitors. All of which you won't find in the massdrop thx aaa. You get cheaper grade components cheaper connectors and a wall wart power supply.

I have no intentions to join this drop since I bought it directly from Matrix (did not want to wait for the drop).
It's a nice amp providing plenty of power.
How powerful it is? Well... at the moment I'm sitting down with my Fostex T60-RP (absolutely awesome headphones, by the way) on my head with a balanced cable plugged into the amp, and the volume nob is at 10 o'clock, on lowest gain setting (yes lowest gain setting of the available three), and the music is quite loud.
Some notes on build quality:
1. Volume knob could definitely improve to be more indicative.
2. Blue led indicating the power is on (I'm not pointing fingers at anyone, but I know some people out there are very picky about LED indicator colors).
3. Gain switch on the back is too tiny in my opinion. It feels like you could break it.
4. Power switch in the back as well (as you all can see).
5. Class A - gets hot as hell!
Sound:
I have no issues with the sound at all. I guess I'm not very picky. Probably more "serious" audiophiles with better ears can share more useful opinions here.
Here is a pic of my setup for you...

search

^^
As you can probably see, I'm feeding it with XLR cables from the Quattro II.

I have the old Matrix-M-Stage 2010 v.2 -- is it worth upgrading to this? My sound card is the Asus Essence STX. My headphones are: Beyer 1990 Pro, Beyer DT880 and soon to come HD6XX and Hifiman 4XX. How do I run these in balanced mode, is it a big difference? What are some other good solid state amp choices for these headphones? Thanks!

I recently bought a new NFB 11.28, and use it with My Senn 650. I have to say it is an amazing dac/amp combo. I do have the Jot dac, and it also sweet to my ears. I found no difference in sound quality between both. and I was using the xlr out to my senn's. the NFB is only 345 shipped, but I dropped 500 on the Jot,. I think that the NFB is much better value, and it offers clean, sound and powerful amp, and I also use it as a preamp to my Darkvoice and it sounds really good. .

People typically go for DIY bottlehead + crack for 650s (or 600s). See if you can fit it in your budget. I have the single ended HPA-3u+ unit and I don't think it pairs well with the 650. It makes the 650 sound analytical and thin and the highs sound a little weird to me. Works great with my HE560s though. If the 6xx is the only pair of headphones you're going to use for sometime it's better to pick bottlehead (apparently).

I didn't get the integrated DAC for the Jot and with a Topping D30 and SMSL SU-8 I haven't found it terribly bright. I think it's the DAC more than the amp. I've found Xduoo and other SMSL DACs and amps brighter in comparison to my two main DACs using the cirrus logic and sabre chips along with a Topping A30, a Magni 3, and the Jot.

Mine is DOA... Any one else having issues???
but, damn..... it is pretty!!!
!!! WAIT !!! Hold the phone, If anyone else is having an issue, they shipped it on 230V . There is a switch on the left rear of the amp that you need to flip for standard US plug Voltage.
Glad that's solved!

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Just about there! We've been in touch with the vendor regarding the group's order and they've let us know that they are still working to gather and pack the group's order for shipment to our warehouse in New Jersey. We will continue to check in with them throughout the fulfillment process and update the group again as soon as everything is en route to us!
Expect another update from us on 8/29 or sooner if something comes up.
If you have any questions, please visit our Help Center (https://massdrop.com/helpcenter).

Awaiting confirmation! We are still in contact with the vendor and just awaiting updated shipment estimates from them. We have a call scheduled first thing tomorrow morning and should get a bit more visibility in regards to when we can expect these in our warehouse.
Expect another update from us on 8/22 or sooner if something comes up.
If you have any questions, please visit our Help Center (https://massdrop.com/helpcenter).

Thanks again for joining this drop! We have submitted the group's order with the vendor for the Matrix M-Stage HPA-3B Balanced Headphone Amp and they are working hard to prepare it for shipment.
As soon as the group's order is ready at the vendor's location, they will send the bulk shipment to our warehouse in New Jersey where our warehouse team will break it up into individual orders and ship them. The current estimated ship date from our warehouse is 8/30.
We will keep the group updated throughout the fulfillment process. You can expect an update from us by the end of the day Pacific Time on 8/15.
If you have any questions, please visit our Help Center (http://massdrop.com/helpcenter).

got this because my Asus Essence STX II is headed for a Taiwanese repair shop, leaving me with just the wimpy amp in the eClaro. Decent dac, but the amp is shite. It's ok that it'll be a while though. I also sent my Alpha Dogs in for an upgrade to Alpha Primes!!! I thought Dan Clark said that was something he'd never do??? Looks like September is going to be a good month!!! Now I just need to save up for a good balanced dac. Any suggestions?

There won't be taxes added when it is shipped to you in Sweden but most likely there will be taxes and handling fees added to the price you've paid at check-out once the product has arrived in Sweden. Before you add the product to the cart please check the website of the Swedish tax office how imports are handled. I assume the price you have paid in USD at check-out will be converted to SEK. Add 25% of tax to it plus handling fees and you'll have a rough idea what it is going to cost you. Once you know this, find out how much this product cost in Sweden or neighboring countries.

I bought the Geek Pulse Infinity off of a guy on Head-Fi and wasn't impressed. The screen was cheap and dim and the knob was crappy as well. I also hated how it took forever to change the volume.
Sold it and wen't and bought a Oppo HA-1. It is such a beautiful device and it sounds amazing.

I liked it a lot. One of the better solid state amps for the HD800. I tried it with the HD800, HE1000 and HE400i. All of those are fairly easy to drive power needs wise, so I never ran into any distortion problems. Ultimately I decided to go tube SE for my HD800, but if I had decided to go balanced solid state this was a contender. Great value for the money. I think it stands toe to toe with the Liquid Carbon.

I wasn't trying to be a smart a## ! There was talk of like three different amps right above your post, so I was not sure. I have the matrix-3b and have been thinking about buying a hd-800 and was wanting to make sure it was the amp you referred to.
Thanks

Looks great for the price if you need a balanced amp, but going from the advertised specs this seems to have a lot of distortion as power levels rise...
Has anyone here used this amp before? How does it sound? And what headphones did you use it with?

In my experience the HE-6 needs an amp that can do at least 5w in to 32ohms--it basically needs a speaker amp level of power. 3.8w into 33ohms isn't going to cut it.
I know lots of people who use Nelson Pass design DIY speaker power amps to feed the HE-6. It sounds absolutely heavenly when properly powered. It still competes (and possibly wins) for the best headphone in existence for me.